1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to a plasma coil and to a processing tool incorporating the same.
2. Description of the Related Art
Physical vapor deposition, reactive ion etching, chemical plasma etching and physical sputtering represent just a few of the potential uses for plasma processes in semiconductor device fabrication. Plasmas are usually created by ionizing a gas or gaseous mixture to produce concentrations of free electrons, ions and neutrals. Most conventional plasma generating tools induce the initial ionization of the gas or gaseous mixture and provide the subsequent maintenance of the glow discharge by exposing the gas to an electric field. Some conventional plasma tools utilize a DC diode configuration to supply the electric field. Others utilize a radio frequency (xe2x80x9crfxe2x80x9d) diode configuration in which the electric field is generated by passing an alternating current through a conducting coil. The frequency of the voltage signal is commonly 13.56 MHz, although some systems have been developed to function in the low GHz and sub-MHz ranges.
One conventional plasma tool utilizing a radio frequency system operating at 13.56 MHz includes a low pressure chamber in which a semiconductor wafer is placed. A quartz plasma plate or window is seated at the top of the chamber. A conducting plasma coil is positioned above the quartz window. The coil consists of a single winding, planar coil that has a plurality of outer turns or windings and a central sub-winding or segment. The central sub-winding is positioned such that there is a void in the central portion of the coil. Power is supplied to the plasma coil by way of a rf power source and a tuning circuit that consists of an impedance matching network and a resonance frequency tuner. The coil is connected in series to the matching circuit. In this regard, a bridge is established between one of the outer turns and the inner coil sub-segment, and the sub-segment itself is, in turn, connected in series to the tuning circuit.
Manufacturing experience has revealed an operational shortcoming associated with this conventional plasma tool. After a few hours of operation of the tool utilizing fluorine-containing chemistries, a polymer residue forms on the underside of the quartz plate. Although the residue tends to form on every region of the underside of the plate that is not physically overlapped by a portion of the plasma coil, the residue tends to form with greater thickness and speed in the portion of the plate that corresponds to the central void of the plasma coil. The mechanism by which the residue forms in the central portion of the quartz plate is thought to be the result of a significant variation in the electric field generated by the plasma coil across the diameter of the quartz plate. In particular, the void region of the coil exhibits a much lower electric field intensity. This diminished electric field intensity in the vicinity of the central portion of the quartz plate is thought to result in fewer ionic collisions with the underside of the quartz plate during plasma processing which might otherwise prevent or retard the formation of the polymer residue.
The formation of the polymer film, particularly within the central portions of the quartz plate, presents two pernicious side effects. The first is the need for more frequent cleanings of the plasma chamber. Any cleaning of a plasma tool ordinarily involves shutting down the tool, breaking open the chamber and cleaning the various components therein. This involves both operator cost as well as diminished product throughput. A second side effect is associated with potential contamination of semiconductor workpieces. Flecks of the fluorine-based polymer residue can break off during subsequent processing of a semiconductor wafer. These unwanted particles of polymer can fall on critical circuit structures of a semiconductor device and lead to yield and performance problems.
The problem of fluorine-based polymer residue build-up presents special difficulties in processes that utilize processing chambers containing aluminum structures and surfaces. Aluminum-fluorine residues tend to be chemically unreactive, and thus resistant to plasma cleaning processes. Thus, conventional waferless plasma clean steps may not adequately remove such chemically stable compounds as aluminum fluoride, for example.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a plasma coil is provided that includes a first conductor coil and a first conductor plate coupled in series to the first conductor coil.
In accordance with another aspect of the present invention, a processing apparatus is provided that includes a chamber that has an insulator plate. A plasma coil is positioned above the insulator plate and has a first conductor coil and a first conductor plate coupled in series to the first conductor coil. A first radio frequency power source is coupled to the plasma coil.
In accordance with another aspect of the present invention, a plasma coil is provided that includes a first conductor coil that has a plurality of turns. An innermost of the plurality of turns terminates to define a central void portion and an outermost of the plurality of turns defines a peripheral portion. A first conductor plate is positioned in the central void portion of and coupled in series to the first conductor coil.
In accordance with another aspect of the present invention, a method of manufacturing is provided that includes introducing a processing gas into a processing chamber that has an insulator plate. A plasma coil is positioned proximate an external surface of the insulator plate. A plasma is excited in the processing chamber by applying radio frequency power to the plasma coil. A footprint of any residue forming on an internal surface of the insulator plate is determined. A conductor plate is formed that has a footprint that approximates the footprint of the residue. The conductor plate is coupled to the plasma coil in series whereby the conductor plate is positioned proximate the external surface of the insulator plate and adjacent to the residue.
In accordance with another aspect of the present invention, a method of manufacturing a plasma coil is provided that includes providing a coil with an outer arcuate segment and an inner segment connected in series. The first segment is removed and a first conductor plate is coupled in series to the outer arcuate segment in place of the inner segment.